Ultraviolet (UV) liquid disinfection has been long known to effect micro-organisms. The illumination of flowing liquid with UV light may cause inactivation of water-borne micro-organisms exposed to the light, provided that the light intensity and exposure duration are above a minimum dose level (often measured in units of miliJoules per square centimeter).
The UV exposure may initiate a photochemical reaction which effectively damages their DNA molecules to such an extent that cell division, and thus multiplication, can no longer occur. The relative effectiveness of UV light wavelengths for this process is known as the germicidal action spectrum. There are a wide variety of micro-organisms that vary in their structure and accordingly in their sensitivity to UV.
The selection of UV light characteristics and other parameters of the disinfection process, such as light intensity, light wavelength and duration depends primarily on the UV light doze necessary to achieve a required reduction in the number of specified micro-organism types (“kill rate”, usually measured in terms of logs). Different minimum doze levels (UV exposures) are required for different micro-organisms to achieve a certain kill rate. The necessary UV doze level for many applications ranges between 10 mJ/cm2 and 100 mJ/cm2.
Further, for certain applications, for example, aqua agriculture applications, it may be desirable to inactivate one type of specified micro-organisms while keeping intact another type of s micro-organisms. Accordingly, the UV disinfection process should be monitored and controlled to guarantee that under changeable operating conditions such as flow rate of the liquid and UV light transmission, the ultraviolet dose would remain within a desired range suitable for the specific required application.
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